Heretofore, for example, in Patent Document 1 and the like, various piezoelectric bulk acoustic wave elements each using a piezoelectric thin film have been proposed. In Patent Document 1, as a method for manufacturing a piezoelectric bulk acoustic wave element, the following method has been disclosed. First, a sacrificial layer is provided in a recess portion of a substrate. Subsequently, a piezoelectric thin film sandwiched between a pair of electrodes is formed so as to cover the sacrificial layer. Next, the sacrificial layer is removed by etching. It has been disclosed that a hydrofluoric acid is used to etch the sacrificial layer.
In addition, Patent Document 2 has disclosed a piezoelectric thin film formed of an aluminum nitride thin film containing scandium. It has been disclosed that the piezoelectric thin film formed of an aluminum nitride thin film containing scandium has a preferable piezoelectric response performance.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-140075
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-15148